Suppose a civilization which had domestic flying dragons at ancient time, just like other common stories here. My question is: would that civilization have cars, planes and ships?

Initially, I think the world would have no cars, planes, ships, and even public transport facilities. My idea is, if I want to go somewhere, why do I need a plane in stead of hiring a dragon? And what is the motivation to invent a plane or car if I can sit on a dragon and then visit everywhere? Does the world with such dragons need planes, cars or ships actually? If so, what is the motivation to invent them?

$\begingroup$Earth had "no cars, planes, ... and even public transport facilities" for the first 5000 years of human civilization. Why should that be any different "with dragons"?$\endgroup$
– RonJohnMay 26 '17 at 6:56

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$\begingroup$My thoughts exactly. Horses were quite popular - until the railway came along and took the long distance travel & freight business, then the internal combustion engine took everything else. Like the horse, your dragons will probably survive as a rich man’s play thing$\endgroup$
– MawgMay 26 '17 at 8:23

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$\begingroup$Have you ever even tried to find a parking space with a dragon? Those things are massive and eat people walking by. Dragons should be used for sporting purposes only (take Dragon ball or something) and are not something every family should own. Also, planes are much faster than dragons. If you want to deliver your fresh fish to some rich, continental city, I would heavily advice vs using a dragon or some other kind of creature - they are simply not fast enough. Just ship it by air or do the car drive$\endgroup$
– Raditz_35May 26 '17 at 8:31

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$\begingroup$Do dragons want to be ridden? If not, flying in a plane might be a much safer idea. If so, I wouldn't want to be selling planes with the Draconic Transportation Union breathing down my neck.$\endgroup$
– gmathtMay 26 '17 at 12:28

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$\begingroup$Have you any idea how expensive it is to own a dragon? Gotta feed that brute a fresh virgin princess at least weekly...$\endgroup$
– EvilSnackMay 27 '17 at 1:52

10 Answers
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I believe mechanical means of transportation would still be developed.

As a basis for prediction, consider the case of the horseless carriage. Why bother inventing a car when you already have horses?

The answer comes from the cost of ownership (space, feed, water, manpower/expertise, equipment) and the significant time investment needed to raise, train, breed, and maintain a stable of horses.

At some point it becomes more economical to use a machine than to support a living creature.

The requirements for raising a dragon are likely more complex and costly than raising a horse, so the same economic pressures would apply. Said pressures would be especially strong in any mythos where dragons are exceptionally long-lived and thus require significant time to rear, where they are potentially dangerous (introducing fire-damage liability), or where they are carnivorous and thus require more costly investment to be kept fed.

If anything, having an animal that predates a mechanical means of transportation might escalate the rate at which such transportation is developed. Consider that horseless carriages were able to take advantage of technical developments (wheel axles, cobblestones), trade and transportation infrastructure (highways and roads), and traffic laws all of which were developed originally to facilitate the travel of horse-drawn carriages.

A civilization with flying transportation that predates the invention of airplanes and balloons would be more likely to establish airport analogs at an earlier stage in their development, as well as develop laws and occupations concerning air travel which would ease the introduction of and possibly the transition to mechanical air travel. They'd also introduce inventions associated with air travel (like parachutes) and uncover scientific principles (such as those related to flight or meteorology) at an earlier stage which would increase the relative safety of mechanical air travel upon its inception.

$\begingroup$I think the analogy is good, but it misses a central ingredient - it's straightforward to go from horse to horseless-carriage, however we're still not at a technological stage where all the capabilities of dragon-borne transport are fulfilled despite more than a century of aviation. This gap may mean flying tech would be a non-starter.$\endgroup$
– vivriMay 26 '17 at 4:03

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$\begingroup$@vivri hogwash. The desire to fly without the need to feed and care for fire-breathing carnivores of limited speed and carrying capacity would, as Thriggle noted, "escalate the rate at which such transportation is developed". And the notion that you can "sit on a dragon and then visit everywhere" is patently absurd: you've got to feed it, "park" it somewhere, have "traffic control", and even if it has a long range, you don't while sitting on a dragon.$\endgroup$
– RonJohnMay 26 '17 at 4:50

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$\begingroup$@jamesqf, if the question says the world has dragons then it has dragons and all that implies, they can fly, breathe fire (or otherwise) and carry significant cargo, how else would they get their hordes back to their lairs?$\endgroup$
– SeparatrixMay 26 '17 at 7:09

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$\begingroup$@vivri remember how the first cars were slower than horse carriages? That didn't stop us from pursuing them as an alternative.$\endgroup$
– John HamiltonMay 26 '17 at 7:46

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$\begingroup$Relating to your final paragraph: I can see that a civilization with dragons might well develop gliders very early on, as an analogue to carts for working with horses: a glider could be tethered to a dragon and used to transport materials that are too bulky for the dragon to carry directly. This could potentially make powered flight much easier to discover...$\endgroup$
– JulesMay 28 '17 at 3:19

While domesticated dragons would be an extremely quick method of transportation, there are several important limitations that must be kept in mind.

They are living creatures. This sounds kind of obvious but needs saying as it combines quite a few problems, such as the need to eat and rest. A car would probably be a lot cheaper to own than a full grown dragon. While you can argue that point as dragons don't need to be replaced every few years, they will also have medical expenses

Size (1). Dragons are big. Yes, you may have some personal dragons which will be smaller and faster, but small will be a relative term here. Keep in mind that horses, the most common riding animal can weigh over 2,000 pounds (900 kg) and eat up to 30 pounds (13 kg) of hay per day plus forage. Your dragons will likely be much bigger if they are meant to carry more than a couple of passengers at a time. This makes them unaffordable to the average citizen.
Another size related issue will be housing. As I said, your dragons will be pretty big so you will have to find a way to house them. Think of a dragon the size of a passenger jet. Now realize that the dragon will need an even larger hangar, and will consume fuel (food) even when not working.

Size (2) As big as you make them, they won't be big enough. Yes I just got through listing the disadvantages of being too big, but it's still true. In 2002 there was a total of 16 billion tons transported. That averages into almost 44 million tons daily. In the US alone. In 2002. An eagle is the strongest real bird, it can only lift four times it's own weight in flight. If you use that as your base (not very realistic as the average that a bird can fly with is closer to half it's weight) you still need a LOT of Huge dragons flying all over the place. You cannot have an economy that is dependent on dragons as transport afford the feeding of a fleet needed over a decade ago.

Exploration.
While my previous points were more focused on the disadvantages of dragons, the next two are more related to why someone will come up with an alternative.
As stated in reason 1:Dragons are living creatures. Therefore they need to sleep, therefore they are extremely unsuited for an exploration across the sea, as well as long fishing trips. Boats are still a necessity that dragons haven't supplied.

Common use.
One of the things that made the car so popular was that it gave the middle class, who couldn't justify housing and feeding a horse year round freedom to go where they wanted when they wanted to. Due to point 2 as well as the lift limits of a flying creature, this factor is even more in play in your world, as the costs of a family sized dragon would be astronomical to the average citizen. This would come into play much later than the boats though, due to being a luxury not a necessity.

$\begingroup$2000 lbs is really about the upper limit for a large draft horse. A typical riding horse would be in the 900-1200 lb range.$\endgroup$
– jamesqfMay 26 '17 at 5:50

$\begingroup$This all assumes dragons are totally physical and aren't magical at all, which the question didn't specify. If they do have magical components, then a lot of the size and payload concerns are alleviated.$\endgroup$
– Azor AhaiMay 26 '17 at 21:17

In fantasy settings, the users of Dragons are the very important, rich, and powerful, and occasionally the lucky protagonist for whom everything in the world is a novelty. Further they are seldom kept like horses, writers deal with their size by letting them run free and come when needed.

I don't think the dragons "scale" (pun intended!). In the USA, there are about 254 million cars for an adult population of 242 million; slightly over one per adult. Only 8% of households have no car at all. My wife and I each own a car, parked in our garage, sitting quietly and requiring zero food, shelter or entertainment for weeks on end if we decide to go on a vacation, or if I leave on assignment or for a conference.

Our residential land doesn't have enough grass to keep alive a dog-sized goat; much less two full grown dragons.

What would food costs be for two dragons?

As earlier answers say, machines are just cheaper. I am in the AI and automation field: Manufacturing robots in America, like those making cars and many other products, currently cost roughly 25c per operating hour for their life, that include the capital cost (initial price of the robot), all fuel, downtime for maintenance, and all repairs. Twenty five cents per hour! That is why they are replacing workers, even overseas workers.

Machines are just cheap, their fuel is cheap, they have no emotions and feel no pain, they can be scrapped, warehoused or sold at will without facing any moral dilemma. I am not being cruel to leave my car parked at the curb, exposed and freezing, in a raging blizzard.

In terms of providing service to humans: Machines are just better, enslaving animals creates (for most modern Americans at least) moral dilemmas about the treatment of the work animals, beating them or otherwise causing them pain, misery or death (for example by exposure to harsh weather, cold, heat, desert environments), dealing with their injuries and illness, feeding them, using them for food, disposing of them. Nobody is morally outraged if you break the axle on your tractor trying too hard to pull a tree stump out; it was just a tool. If that is a horse's leg, and you were beating him bloody to make him pull harder, and then you have to shoot him in the head: Now people start to feel moral outrage.

$\begingroup$This is very nitpicky, but you just said you have two cars in your garage, but them claimed they need no shelter. What is a garage (primarily) except to be a shelter for cars? I would add, though, that some have made the humorous observation that many people leave their $30,000 cars parked in their driveways in order to fill their garages with useless junk. ;)$\endgroup$
– Charles BurgeMay 26 '17 at 20:14

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$\begingroup$@CharlesBurge In context I am speaking in comparison to living animals: Cars don't need shelter like animals do; a car isn't going to freeze to death or die of heat stroke. It isn't uncomfortable being rained on or hailed upon or caught in a dust storm. I put my cars in the garage because I don't want teens messing with them, or drunk drivers bumping into them. That said, I have sometimes left my car on the street overnight because my garage was temporarily storing something else; like a refinishing project.$\endgroup$
– AmadeusMay 26 '17 at 21:10

$\begingroup$"or hailed upon or caught in a dust storm" Pictures of cars damaged by hail are easy to find on Google, and a sandstorm would certainly mess up a car . Still, they are a whole lot more durable than draft animals: barns are a lot bigger and more complicated than carports.$\endgroup$
– RonJohnMay 26 '17 at 22:43

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$\begingroup$@RonJohn I will repeat, I am talking about in comparison to living animals. There is scant emotion and no moral outrage by others if you let your car be dented or totaled by the weather; there is plenty if you leave your dog tied to a tree and shivering in the snow. My car does not inherently need shelter. If I want to save money, then I need shelter for my car, my car doesn't care. It is not capable of that, or being in misery or suffering like a dog, a horse, or a presumed dragon. Those all need shelter from the elements, lest they suffer.$\endgroup$
– AmadeusMay 26 '17 at 23:23

$\begingroup$@Amadeus: Horses do not inherently need shelter. Lots of wild ones hereabouts that live their lives with no more shelter than nature provides. Our domestic ones have simple run-in shelters that they can use to get out of the weather, but are happy to spend most of their time out in the field. Fancy barns & stalls are an unnatural, and IMHO unhealthy, environment. I imagine the same would be true for dragons. They spend most of their time out doing the draconic equivalent of grazing, but come when you call them.$\endgroup$
– jamesqfMay 27 '17 at 4:37

Let's say your dragon is reasonably large for an animal, about the size of a DC-3. It can carry about 5000 kg of cargo, can cruise at 300 km/h for eight hours between meals, and can land in any reasonably large field. It requires one rider to control it in the air and one handler to take care of its needs on the ground.

By medieval standards, this is a rather impressive beast. It can carry the cargo of four or five freight wagons, and can reach anywhere in a reasonably-sized country in less than a day. It doesn't have the raw capacity of a merchant ship, but the ability to make a few dozen hops across the English Channel in the time a ship could do a single round trip more than makes up for it. Dragons would be the transportation of choice for virtually everything except in-city movement (where the lack of landing fields prevent their use) or cargoes that can't be broken down into dragon-sized loads.

Now, you hit the industrial era and your manufacturing economy starts growing. Instead of moving a wagon-load of coal to a blacksmith's shop a few times a year, you're moving 30,000 tons of coal to a large-scale smelter every day. To do this by dragon-back, you'd need 6000 dragons, with 6000 riders and 6000 handlers. In constrast, a heavy-duty freight train could do that with just an engineer and a mechanic.

Or, you're moving 120,000 tons of goods from factories in America to European stores. You could hire 24,000 dragons to do the job, with their 48,000 human assistants, or you could get a Triple E class container ship to do it with 19 people.

The problem with dragon-based transport is that it's very labor-intensive compared to the mechanized alternatives, and you can't really reduce that labor requirement through technological innovation.

$\begingroup$Yeah -- the other downside is speed. A DH8D (DHC-8-400 aka Q400) can cover 2400km with a 5000kg payload (see PDF page 71), and do so in about 3 hours vs the 8 your dragon takes, while being able to get in and out of most reasonably sized airports. (It does take one more pilot + a few more ground handlers to service, but considering you'd need 2 dragons to do the job of one Q400...it's mostly a wash anyway)$\endgroup$
– ShalvenayMay 27 '17 at 15:54

$\begingroup$You also forgot to mention how badly a dragon would compare to a much larger aircraft -- a 747-8F needs not many more people to service it than the Q400 from my previous comment, while carrying the load of 26 dragons (130,000kg payload) over 7200km (3x the distance) at 3 times the cruise speed of a dragon (900+km/h @ 30,000'+). That adds up to 78 dragons to match 1 747-8F. It also shrugs at weather conditions that'd keep the dragon's feet firmly planted on the ground...$\endgroup$
– ShalvenayMay 27 '17 at 16:09

$\begingroup$@Shalvenay: You're forgetting that to take off and land that loaded 747, you have to factor in the cost of about 7,500ft / 2,300m of high-strength paved runway :-)$\endgroup$
– jamesqfMay 29 '17 at 17:23

$\begingroup$@jamesqf -- that's mostly a function of the 747 being a civil airliner and having civil airliner landing gear -- military transports are routinely equipped with landing gear systems that are capable of handing much worse conditions.$\endgroup$
– ShalvenayMay 29 '17 at 17:28

It's arguable whether flying economy is more comfortable than wrapping your legs round an enormous hard scaly moving cylinder would be, but any other class, and certainly any car ever made would be nicer to travel in.

Also, unless your dragons have roofs, no-one flying to a fancy party on a rainy day is going to want to use them.

$\begingroup$I'd add that just because we can ride dragons, doesn't mean we want to. I know plenty of people who are loath to get into a perfectly safe jet liner and they'd really freak out if asked to sit on a dragon from Heathrow to Paris.$\endgroup$
– StephenGMay 26 '17 at 15:44

$\begingroup$I think that comfort could be a factor in adoption, but only after the technology is mature; the Kitty Hawk probably wasn't too comfortable. One difficulty with this question is that we're left to make assumptions about what dragons can and can't do. Maybe in this world one could snuggle up in their comfy brooding pouches or sit in their mouths (I hear they have central heating). If their flight isn't dependent on aerodynamics (say that they breathe fire and are more like hot air balloons or dirigibles), maybe some kind of cozy palanquin could be set up on top, like riding a luxury elephant.$\endgroup$
– ThriggleMay 26 '17 at 15:45

$\begingroup$Car might indeed be more comfortable option; but riding a dragon would surely be preferred to Economy seat in your average airliner ...$\endgroup$
– Matija NalisMay 26 '17 at 18:21

$\begingroup$@Thriggle : "one could snuggle up in their comfy brooding pouches or sit in their mouths" - Jeepers, that's worse than riding on the outside ! My can't-fly-won't-fly cousin would never go near an airport again if asked to sit in the dragon's mouth, please. Neither would I ! And a brooding pouch sounds yuch.$\endgroup$
– StephenGMay 26 '17 at 23:05

$\begingroup$@StephenG: For a lot of those people, it's not safety or the perceived lack thereof, it's being crammed into an uncomfortably small space with a hundred or so strangers and subjected to various indignities. I wouldn't do that for anything much short of a life-or-death reason, even if the sardine can never left the ground, while I quite enjoy flying in my own plane.$\endgroup$
– jamesqfMay 27 '17 at 4:41

Well, hey, we developed cars even though we could just sit on a horse. And we developed machines to do all kinds of things that we could just pay a person to do. So I don't see any "suppose" in your question, except that you're talking about automating the job of a dragon, rather than automating the job of a horse or a person. The motivations would be exactly the same, plus the fact that having dragons around is much more risky than having horses.

I don't see how dragons would have a measurable effect on the development of transportation. The main reasons are:

Availability -- assuming you have less dragons than humans in your world, there is always someone without a dragon who needs another mode of transport. Look at cars in our world: Sufficiently wealthy countries trend towards a 1:1 ratio between people and cars.

Load -- we still use ships, trains and trucks because lifting things by airplane is not only expensive, load capacity is also limited. The same will be true of your dragons. A nice ship will be able to carry several times what even the largest dragon can carry.

Convenience -- there are places dragons can't go. Horses need less food. Waggons are useful even in dense forests. An ox can pull a cart and when older you can kill it for meat. A dragon will not be the best option in all cases.

$\begingroup$Points 1 & 3 rely solemnly on the premise that we are discussing Dragons, while the question inquires about unspecific large flying creatures, and Dragons are given only as an example. This creature doesn't have to be a scarce reptilian which is hard to feed, it can be a common, huge flying insect which feeds of flora.$\endgroup$
– FingolfinMay 26 '17 at 10:21

$\begingroup$@Fingolfin - but if the OP is looking for reasons to justify having both planes and large flying creatures which can take a mount, then Tom's points are completely valid.$\endgroup$
– colmdeMay 26 '17 at 11:22

$\begingroup$Re "1:1 ratio between people and cars", I think it could well be higher than that. I currently have two (well, a car and a truck), and at times have had more, plus motorcycles, airplanes, and horses. Dragons/unspecified large flying creatures probably need specialized landing areas, just as my airplane did. It's all about using the right tool for the task at hand.$\endgroup$
– jamesqfMay 26 '17 at 20:53

$\begingroup$@Fingolfin - size and feeding requirements are related. If you have enough critters that are fairly big, some grass at the edge of the road won't be enough.$\endgroup$
– TomMay 27 '17 at 8:48

$\begingroup$@jamesqf yes, but on average. I didn't own a car for 15 years, because living in the center of a city, I didn't need one (I rented occasionally). Plus there are children, old people, etc. I think a 1:1 average is a fairly good estimate, but I didn't google to check.$\endgroup$
– TomMay 27 '17 at 8:50

I do agree with the top-answers, but so far most seem to assume you can deal with dragons just like in games: you call, they come, you ride where you want, they vanish and come whenever you need them.
If we consider them to be realistic animals, they need a lot of attention to behave like you want them to (aside from the logistics like parking and feeding others have already addressed).

Look at how much time horse riding realistically takes. Someone has to breed the horse, domesticate it and train it. You as the owner need to learn to ride it and you will need some time to get accustomed to your horse, eh dragon.

Then again, horses are quite peaceful creatures - being "veggies" and therefore rather defensive than aggressive. Dragons are typically considered on the other end of the spectrum, they are carnivores/predators. This makes training harder, and the everyday risk higher. Consider having a lion around. Better make sure he's never hungry when you just need him or your daughter thinks she needs to borrow him for a quick ride.

Dragon riding could be a profession for special tasks, like the original cowboys did ride a lot because of the cows ;) There might be dragon riders that carry around cargo in remote areas, in jungles etc. Not that there are that many left in our time, but they could fill a nice gap where planes and cars cannot properly operate and choppers are difficult to maintain, have still limited take-off or too slow when it comes to loading and unloading.

But they wouldn't replace mechanical private or public transport.

As a side note, if your argument includes magic, then the same magic can be used to improve mechanical transportation ;)

$\begingroup$they are carnivors/predators. This makes training harder I don't disagree that a superpredator would be tough to train, but as a counterexample of this, consider the domestication of canines. Check out this passage from the current wikipedia page on the origin of the domestic dog: "It may have been inevitable that the first domesticated animal came from the order of carnivores as these are less afraid when approaching other species."$\endgroup$
– ThriggleMay 27 '17 at 2:32

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$\begingroup$Sure, our best friends the dogs. And still, how often do people have legal trouble, because our "very well domesticated" dogs do bite someone - or just bark at someone. With much larger horses this is way less of a problem (they may however run in front of cars and make more damage than the smaller dogs, while both get hurt or die in the process). Dragons however would be both, huge enough to properly damage "things" and be prone to "bite" and "bark"... or set the postman in flames...$\endgroup$
– Frank HopkinsMay 27 '17 at 2:38

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$\begingroup$Now's there's a story idea: the beleaguered postman who has to dodge the neighborhood's overprotective dragons!$\endgroup$
– ThriggleMay 27 '17 at 2:40

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$\begingroup$And in the end, after many honourable deaths, they will strike a deal - free food for a side-job at the post office. And born are the official post office dragon riders. Who then, in the third part of the trilogy, in a last uphill battle ride against Amazon's drone army.$\endgroup$
– Frank HopkinsMay 27 '17 at 2:49

$\begingroup$@Thriggle and Darkwing I wish this tidbit was a full on answer so I could give it a rep inflating upvote!$\endgroup$
– Paul TIKIMay 27 '17 at 13:31

It will indeed have a large (negative) effect on the development of such transportation means, given the right ecological and geographic conditions.

Some of the other answers discuss the possibility that the maintenance cost of a Dragon is just too high and will encourage humanity to find a mechanic alternative. That may be correct, but
only under the assumption that it has to be a classic fire-breathing, carnivorous, long-living D&D Dragon. It might as well be a peaceful creature which feeds off an abundant plankton-like substance, just like the Blue Whale, or an insect-like creature which feeds off leaves and grass (which in your world, might be extremely large and abundant).

An insect like creature can also carry a weight much heavier than itself, so the issue of mass cargo transport can also be solved. Btw, the classic D&D setting also mentions the fact that dragons levitate by some magical means (since an approx. 20-ton creature can not possibly carry it’s weight in the air even with an approx. 20-meter wing span). So, these magical means may as well allow them to carry a much heavier weight and therefore be used for cargo transportation. Insect-like creatures are also abundant and multiply rapidly, which might solve the supply-demand issue (while obviously can pose a whole new challenge to solve as well).

Ships, however, might prove to be something else. Ships (or boats, at least) were used for fishing purposes since the dawn of humanity. In a world with many seas and costal regions, fishing will be necessary, and that is something which a huge insect/dragon like creature can’t serve for, unless you throw in some aquatic equivalent. In a world with large oceans, a flying creature might be unable to complete a direct flight from one continent to another in a straight line without getting tired, and so large ships will be needed for sailing. Also, even long after the invention of planes, usage of ships for cargo transport purposes has not decreased. If your world reaches the equivalent of modern times in terms of other technologies, there are things which are just too damn heavy for planes to carry, and so will be the case with flying creatures as well - ships will still be needed.

In the bottom line - I do believe that with the right ecological setting, humanity just won’t be motivated enough to invent airplanes or cars, as well as many other inventions which lead to thee discovery of those two. Existence of such tamed creatures might have tremendous implications - If travel is that easy in prehistoric times, the agricultural revolution might not happen at all! Humanity might prefer to keep living in nomadic tribes, travelling at their leisure to warmer places where food is more abundant. If that word’s does not has large oceans, seafaring will stay at boat level, preventing the invention of steam-powered ships and therefore pushing even further away the idea of engine-powered vehicles.

However, if the setting is not right and humanity is pressured by various factors (large water masses, scarcity of flying creatures, high maintenance/mediocre usability of those creatures due to conditions described in 1st and 2nd paragraphs not being met) ant therefore is pushed to find scientific solutions to achieve it’s goals, then eventually the industrial era will arrive, powered by engines - and when you have engines, engine-powered vehicles will arrive.

$\begingroup$It does not have to be scary carnivorous creature, but even if it is herbivorous, it will still eat awfully lot. Flying takes energy, even more so when carrying load, and living creatures are simply not all that efficient in converting food to work.$\endgroup$
– Jan HudecMay 27 '17 at 20:56

$\begingroup$@JanHudec - Again, if making a blue Whale analogy - it can work out in a world containing abundant plankton-like substance. If making a giant insect analogy - it can work out in a world containing huge trees and leaves. The question wasn't about how could these creatures exist - it was how they would affect human transportation, assuming they do exist. I just didn't narrow it down to rare flying carnivorous reptilians, cause why should I?$\endgroup$
– FingolfinMay 28 '17 at 7:48

It seems like your question is why people would go from dragon-riding to cars and boats - that is, why they would develop or transition to "lesser" forms of transportation, why it would occur to them. Once they have them, they'll use them - as several other answers have mentioned, and how the development of planes didn't make cars or ships (or trains) obsolete, due to different niches and different best-uses, so I'm going to focus on the development process itself.

So, I think the development of cars, ships and trains is going to be totally independent of your society's domestication of dragons. And it can be independent because the very beginnings of that development process will likely predate the domestication of dragons. Long before your people develop a relationship with dragons that involves riding them, or hauling cargo with them, your people will be walking all over the place with stuff to get from one point to another. I expect travois, sledges, litters and rafts to be developed to better drag or carry stuff while walking, just like our history.

And it also seems likely to me that dogs and possibly horses will be domesticated before the dragons, just because they're smaller and more approachable and probably easier to domesticate - and feed, especially when there was not a reliable surplus beyond what people need to eat. Horses can eat things people can't, and dogs can eat scraps or vermin when there isn't enough meat, but dragons need to eat meat, and in amounts that will compete with the supplies people will need (flocks and herds), and are likely to be less accommodating about shortages than dogs or horses.

From walking, carrying, and dragging, I would expect the progression to continue through carts and carriages, and eventually to trains and cars. This would be totally independent of dragons, for places where maneuverability is important, like forests or cities, for short distance or small scale (initially), when it would be easier to just take it rather than getting it to where dragons can carry them, and for those who may well not be able to afford (or just prefer not to) hire dragon-dispatch. And there's no reason they wouldn't progress through horse-drawn carts, or bicycles, or other sorts of mechanical work like dog-sleds or horse-drawn plows or donkey powered millstones, and progressing through powered devices like cars or trains for the same reason we did in our history - it is easier than doing it ourselves, and I'd think horse-drawn stuff is easier and more versatile than dragon-drawn gliders for extra mechanical work or even stuff-space when traveling.

Similarly, ships would come from boats, before that rafts, and be useful for fishing, as a basic use - fishing from dragon-back seems somewhat less likely than just traveling, we don't fish from planes, after all. Also, once they've got started it seems like boats and ships may be useful for small areas not worth dragon-flight, like ferries across rivers or ponds, or maneuvering in areas (rivers, islands) were there may not be room for a dragon to land. And when ships get bigger and reliable, they will again be useful when carrying large quantities, and also for exploration (wiser to make sure you've somewhere to land before haring off across the seas on dragon-back).

So I don't think it will ever be about going from dragon riding to crafting cars or ships, I think they will evolve alongside each other. Cars, and carts and sleds will progress from each other, and innovations will happen to make them better suited for their work - in areas or with people when dragon flight wasn't used to begin with. Ships, boats and rafts will similarly come from their own precursors, for use in ways that has never included dragons. I don't think these will be even vaguely in competition with each other until the separate technologies are quite advanced - I mean, there might be a few things in the history of dragon-riding that was horses or ships in our history, mostly in the fast and showy travel options, but by and large there may not be a ton of overlap.

Of course, that's cars and ships. Planes and their development will be heavily influenced by having dragon-dispatch available, and those influences may not be predictable. One the one hand, people will have a better understanding of aerodynamics, and the underlying principles of flight, from having flying conveyance available - making it easier to figure out what would have to be done for human-powered flight to be created. And, kites, gliders or possibly balloons may be available fairly early, towed by the dragons as an equivalent to carts on land. On the other hand, there is something already available in the flying niche, so there will be less pressure to figure out an alternative solution, and possibly less flexibility for innovation - having something that works (dragons), it might be harder to figure out fixed-wing craft instead of trying to replicate dragon or bird style flying.

I do think mechanical transportation, planes, will eventually outstrip dragons as an economy-level workhorse (much like cars outstripped horses),for being more reliable, requiring less maintenance, less fuel or at least fuel which does not compete with humans need for food, and having fewer limitations (or specifically, being able to design around and improve those limitations in a way living beings can't be improved). Also like horses, dragon-flight will likely be maintained at a social level, for ceremony or style, for fun, because people will want them, for speed, perhaps.

As a side note, you were questioning the motivation to invent, when there's an alternative solution already. Well, there are (at least) two basic motivations to invent that having dragon-riding won't touch. One is small, practical, gradual improvements to things used for daily work - for example, things to make a cart ride smoother or less work makes sense if one was using carts for transport, more so than switching to dragon-dispatch and abandoning the (already available and paid-for) cart and whatever reasons one had for using it instead of dragon in the first place. Another reason is, some stuff gets invented or tinkered with just because someone can. There isn't a lot of practical use for, say, snorkeling, or hang gliding, or skateboarding - there are more practical versions available, in scuba-diving, airplanes, or cars (or even bikes) - but they're fun, so people came up with them, and use them, and improve on them. People want to fly, dream of it, and going dragon-back may not scratch that itch (like airplanes do for some but not others) - so someone invents hang-gliding, just because they want to. And that is one more step in the direction of airplanes, even if that ultimate result isn't the reason why they did it.